The invention relates to the delivery of substances from devices, and more particularly, to extending the duration of delivery from diffusional or osmotic devices.
Diffusional and osmotic delivery devices are gaining in popularity as a means of delivering substances, usually but not always drugs, into an environment at a well defined rate which is preset in the manufacturing of the device. Currently, these devices are used most extensively to deliver: therapeutic substances to cattle (U.S. Pat. No. 4,300,558); drugs to laboratory animals (U.S. Pat. No. 4,320,758), or fertility-preventing hormones to humans (U.S. Pat. No. 3,993,073). The devices currently exhibiting widespread popularity, however, are limited to fixed delivery rates. Users have become increasingly desirous, however, to have devices of different delivery rates, or delivery rates which they can adjust themselves.
This problem has been addressed in the prior art, however solutions include manufacturing changes, such as: reformulation of the devices with a different concentration or loading of substance; laminating membranes of different permeability in layered contact with the drug formulation layer; or other such non-adjustable formulation changes which predetermine the substance release rate pattern. An inherent problem is that the user must purchase devices with foreknowledge of the delivery rates he or she will require. To avoid delays, the user would then have to maintain a stock of a variety of devices. Additionally, the user is confined to the release rate characteristics manufactured into the delivery device. Accordingly, what must be provided is a means of allowing the user to alter the release rate depending upon the requirements of the intended use. As a result, the user enjoys the greatest flexibility, and need only stock one device.
An approach to the provision of a separate delivery rate adjustable device is found in U.S. Pat. No. 4,474,575. A separate housing encloses the delivery device, wherein the fluid to activate an osmotic delivery device is additionally provided within the housing. Screws threadably move occluding panels into proximity to the delivery device. This device is useful where a separate activating fluid must be provided, as in the intravenous application illustrated in FIG. 6 of that reference. This configuration is complicated, however, where a separate activating environment need not be provided. Moreover, the device has an attendant bulk which is undesirable in many applications. Moreover, the device cannot be implanted within an animal or human body. Removing the housing in applications where it is not needed destroys the adjustability of the device. Additionally, there are added costs associated with a device of this complexity, which should not be borne by users who have no need for a separate activating environment.
Another approach to adjusting the delivery rate downward is to coat the transport area of the delivery device with an impermeable material, where the material will not function as an activating fluid. Specifically, the material must not be able to permeate the transport wall. Accordingly, solvents cannot be used; thus, the material must generally be a solid at use temperatures, and is heated to allow dip-coating of the transport wall. The selection of materials which are suitable is thus limited in that the melting temperature must be low enough to avoid damage to the wall of the device, which typically has a low melting point itself. In the prior art, paraffin wax has been used as the dip-coating, impermeable material. This technique has a number of disadvantages. A threshold concern is that the dip-coating process, and the material itself, may alter the operating characteristics of the device, rendering the predetermination of delivery rates uncertain. Moreover, the material is not suitable for many of the environments in which the device may be placed. Particularly, paraffin is soft, may be incompatible with the environment of use, may become dislodged in movements of the organism, or may be abraded against internal structures, resulting in the release of material into the organism. In laboratory experiments, this is an unacceptable result. In therapy, it is obviously undesirable to introduce unretrievable foreign material. The use of paraffin or a dip-coating process by the user additionally does not guarantee for accurate predictability. In the dipping process, it would be imperative to maintain the device in a perfectly upright position in order to coat to an exact marking. Further, determining the area of the device which must be covered in order to alter its performance by a particular fraction can be difficult if not impossible to accurately determine outside of the manufacturing facility. Therefore the practice of paraffin or any material dip-coating does not provide the user with an accurate means of altering the release characteristics of a delivery device, nor does the method provide a durable, inert, reproducible, or technically safe device.
It is therefore an object of the invention to provide a means and method for enabling the post-manufacture adjustment of the delivery rate of diffusional or osmotic delivery devices.
It is a further object to provide for quick and simple adjustment of devices already manufactured and in the marketplace.
It is yet another object to provide for adjustment whereby the adjustment device is: securely fastened to the delivery device; does not introduce unwanted materials into the use environment; and provides for accurate adjustment of delivery rate change by the user.